1. Field of the Invention
The present invention relates to a wireless transmitter, a wireless receiver, and wireless communication equipment of CDMA system for digital cellular mobile communication or the like, and more particularly, to ones with which both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) can be operated in a simplified construction and efficient manner.
2. Description of the Related Art
In digital cellular mobile communication, multiple access systems in which a plurality of mobile stations simultaneously connect with a circuit using the same frequency band are adopted. CDMA (Code Division Multiple Access), one of the multiple access systems, is a technique for carrying out multiple connection utilizing spread spectrum communication where a spectrum of an information signal is spread over a sufficiently wide band compared with the original bandwidth in transmission. Thus, CDMA is sometimes referred to as Spread Spectrum Multiple Access (SSMA). As a method of spreading a spectrum, Spread Spectrum-Direct Sequence (SS-DS), that is, a system where an information signal is multiplied directly by a spread series code to spread the spectrum of the information signal.
It is an object of the present invention to provide a CDMA cellular mobile communication system in which both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) methods can be used for transmission and reception of communication signals.
In wireless communication, there are two systems: a system where transmission and reception are allotted to different radio frequencies (FDD: Frequency Division Duplex); and a system where the same frequency is used and transmission and reception are allotted according to time sharing (TDD: Time Division Duplex). As shown in FIG. 9, in FDD, a radio frequency F1 (801) for a down circuit (from a base station to a mobile station) is different from a radio frequency F2 (802) for an up circuit (from a mobile station to a base station). On the other hand, in TDD, which is sometimes referred to as the ping-pong system, the same radio frequency F3 (803) is time shared to transmission/reception to carry out communication.
In FPLMTS (Future Public Land Mobile Telecommunication Systems) which is now being standardized as systems for mobile communication in the next generation with ITU being at the center, 1885-2025 MHz and 2110-2200 Mhz are allotted as radio frequencies for FPLMTS bands. For example, the above two frequency bands are to be allotted to the FDD band and the TDD band, it may be considered that 2110-2200 MHz and 1885-1975 MHz, each having a bandwidth of 90 MHz, are allotted to the FDD band and the remaining low frequency band, that is, 1975-2025 Mhz having a bandwidth of 50 MHz is allotted to the TDD band. In this case, as a cellular wireless system, it may be considered that the two communication systems, FDD and TDD, are operated in the same area and by the same base station.
Accordingly, the present invention provides a CDMA cellular wireless communication system which can operate both FDD and TDD.
According to the present invention, there is provided a CDMA cellular wireless communication system which comprises a base station, a plurality of mobile stations for communicating with the base station, FDD (Frequency Division Duplex) communication means between the base station and the mobile stations using different radio frequencies for transmission and reception and TDD (Time Division Duplex) between the base station and the mobile stations using a same frequency for transmission and reception between the base station and the mobile stations.